Filtration centrifuges peeler

Rotary-Siphon Peeler Centrifuges In this type of centrifuge, a partial vacuum is drawn on the outer diameter or tne filter such that the filtrate flows through the cake under both centrifugal force as well as a positive pressure difference of about I atm or less. Thus, a higher rate of filtration takes place due to the increased driving force. 

Medium-rate filtration is accomplished with vacuum drums or disks, or peeler-type centrifuges. 

The solids distribution profile may tend to be parabolic with thicker cakes near the bottom of the basket, tapering down toward the top, since the G-field is perpendicular to the force of gravity. This is especially true with fast-sedimenting solids that will settle toward the basket bottom before the slurry is fully accelerated by the basket. The coarser solids can settle toward the basket bottom, while the finer solids deposit preferentially toward the top. This can result in uneven filtration resistance in the cake, affecting the wash pattern and efficiency of the wash. In cases where this is a concern, a rotating feed cone may be better for even distribution, or a horizontal peeler centrifuge may be better suited to the application. 

The increased capacity of peeler centrifuges has been obtained by the use of a siphonic action to enhance the effective pressure differentials, as shown in Figure 58.18. Here the filtrate is not centrifuged through the drum perforations immediately after penetrating the filter cake, as occurs in standard peeler centrifuges, but collects behind the filter cloth. This chamber is connected to a ring cup that behaves... 

FIGURE 58.18 Peeler centrifuge with rotary siphon (1, slurry 2, feed pipe 3, cake 4, siphon holes 5, basket 6, slurry 7, wash pipe 8, peeling device 9, peeling knife 10, solid 11, solids chute 12, filtrate 13, liquid layer 14, siphon pipe). (From Mitsubishi Kakoki Kaisha, Ltd., licensed by Kracess Maffei Process Technology AG. With permission.)... 

One of the most commonly used solid-liquid separation methods in crystallization processes is centrifugal filtration, such as continuous pusher and batchwise peeler centrifuges shown schematically in Figure 64.10. A manufacturer of centrifuges used in crystallization processes is KMPT AG [52]. In addition, Nutsche filters, frame pressure filters, and belt filters have also been used. Most of these filters have a possibility of cake washing which is important for the final purity as discussed earlier. 

Figure 6.10 Schematic diagram of a peeler centrifuge cycle, (a) Filtration (b) displacement washing (c) deliquoring (d) cake discharge by plough.

The peeler centrifuge of Figure 3.34 can also be sealed against vapour loss, or given a nitrogen blanket to protect the cake (or filtrate) from air oxidation. 

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